Aerial system and vehicle for continuous operation

ABSTRACT

An aerial vehicle having a vision based navigation system for capturing an arresting cable situated at a landing site may comprise a fuselage having a propulsion system; an arresting device coupled to the fuselage, the arresting device to capture the arresting cable at the landing site; a camera situated on the aerial vehicle; an infrared illuminator situated on the aerial vehicle to illuminate the landing site, wherein the arresting cable has two infrared reflectors situated thereon; and an onboard vision processor. The onboard vision processor may (i) generate a plurality of coordinates representing features of the landing site using an image thresholding technique, (ii) eliminate one or more coordinates as outlier coordinates using linear correlation, and (iii) identify two of the plurality of coordinates as the two infrared reflectors using a Kalman filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims priority to U.S.application Ser. No. 14/213,450, filed on Mar. 14, 2014, entitled“Aerial System and Vehicle for Continuous Operation,” which claimspriority to U.S. Provisional Patent Application No. 61/851,866, filed onMar. 14, 2013, entitled “Aerial System and Vehicle for ContinuousOperation,” both of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to systems and methods for use withUnmanned Aerial Vehicles (“UAVs”) and Unmanned Aerial Systems (“UASs”).More specifically, the present invention relates to systems and methodsfor enabling the operation of an autonomous, self-charging aerialvehicle surveillance system.

BACKGROUND INFORMATION

The use of Unmanned Aerial vehicles (“UAVs”) and Small Unmanned AerialSystems (“SUASs”) has grown in recent years and such UAVs and SUASs areemployed in a wide variety of applications, including both military andcivilian uses. In some applications, a UAV or SUAS may be required tomaneuver quickly, or in tight spaces, over a wide range of speeds.Accordingly, several efforts have been made to improve UAV and SUASperformance to yield a fully autonomous UAV system.

For example, U.S. Pat. No. 6,960,750, to Doane, discusses an opticalsystem and method for positioning a first object with respect to asecond object, such as a refueling aircraft and an unmanned air vehicle,including a pattern of reflectors, an optical receiver, an opticaltransmitter, and a processor. U.S. Pat. No. 7,318,564, to Marshall,discusses a surveillance aircraft recharging system based on energycollection by magnetic induction from the current flowing in a randomlyselected alternating current transmission line conductor. U.S. Pat. No.7,714,536, to Silberg, discusses a method and apparatus for chargingenergy supplies in a UAV. U.S. Pat. No. 8,167,234, to Moore, discusses amicro air vehicle (MAV) that comprises features that emulate insect-liketopology and flight, including a dangling three-part body (100 a, 100 b,100 c); wing-like, dual side rotors (107, 107 a) positioned to eitherside on rotor arms (103) providing tilt and teeter motions to vectorthrust and allowing crawling along improved surfaces; and elevators(101) that approximate the center of gravity and center of pressurecontrol employed by insects via the inertial reaction and aerodynamicinfluence of a repositionable abdomen. U.S. Pat. No. 8,172,177, toLovell, discusses a stabilized UAV recovery system. United States PatentPublication No. 2003/0222173, to McGeer, discusses a method and anapparatus for capturing a flying object.

While a number of UAVs and UAV systems are disclosed through the abovereferences, existing UAVs and UAV systems are deficient in at least tworespects. First, existing UAVs are not entirely self-sufficient andrequire routine upkeep, such as charging and/or refueling. Second,existing UAVs are generally concerned only with the cable capture (e.g.,landing), but do not consider both the autonomous capture and release ofthe vehicle. Accordingly, the present application provides systems andmethods for providing a self-charging UAV and UAV system capable ofautonomous capture and release.

SUMMARY

The present disclosure endeavors to provide systems and methods forenabling the operation of an autonomous self-charging aerial vehiclesurveillance system.

According to a first aspect of the present invention, an aerial vehiclesystem for gathering data comprises: a waypoint location, wherein theWaypoint Location comprises an arresting cable; a ground controlstation, wherein the ground control station comprises a charging cable;an aerial vehicle, wherein the aerial vehicle comprises an onboardbattery, a capturing hook and a sensor payload for generatingsurveillance data; wherein the aerial vehicle is configured toautonomously travel between the Waypoint Location and the ground controlstation; wherein the aerial vehicle is configured to couple and decouplewith the arresting cable via the capturing hook; wherein the aerialvehicle is configured to perch from the charging cable via the capturinghook; wherein the aerial vehicle is configured to electronically coupleand decouple with the charging cable via the capturing hook tofacilitate charging the aerial vehicle's onboard battery.

According to a second aspect of the present invention, a capturing hookfor engaging a cable during capture and release of an aerial vehiclecomprises: a first gate pivotally supported at a first end by a baseportion and movable between (i) a closed position and (ii) an openposition; a first return spring biasing the first gate to the closedposition; a second gate pivotally supported at a first end by the baseportion and movable between (i) a closed position and (ii) an openposition; a second return spring biasing the second gate to the closedposition; and a latch device comprising a movable locking part biased bya return spring to a locked position to lock the second gate in theclosed position.

According to a third aspect of the present invention, a vision-basedaerial vehicle navigation system for capturing an arresting cablecomprises: a camera; an infrared illuminator positioned on an aerialvehicle; two or more infrared reflectors positioned on an arrestingcable; and an onboard vision processor configured to calculate thecenters of each of said two or more infrared reflectors.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention will be readilyunderstood with reference to the following specifications and attacheddrawings, wherein:

FIG. 1 illustrates an example Continuous Operation System;

FIG. 2 illustrates a block diagram of a UAV communicatively coupled witha Ground Control Station;

FIGS. 3a and 3b illustrate an example UAV for use with a System;

FIGS. 4a through 4d illustrate example cable capture and releasemaneuvers;

FIGS. 5a and 5b provide an enlarged view of an example arresting device;

FIGS. 6a through 6e provide enlarged views of the arresting device'scapturing hook during the cable capture and release maneuver of FIGS. 4athrough 4 d;

FIG. 7 illustrates a Ground Control Station 102 positioned on a rooftop;

FIG. 8 illustrates a schematic diagram of a Ground Control Station 102;

FIG. 9a illustrates a block diagram of an example vision-basednavigation system;

FIG. 9b illustrates an example process of analyzing an image using avision-based navigation system;

FIG. 10a illustrates a cross-sectional view of a charging cableelectrically coupling with a conductive contacts;

FIG. 10b illustrates an example configuration for positioning conductivecontacts on an arresting device capturing hook; and

FIG. 11 illustrates the geometry of the guidance elements in the cameraframe.

DETAILED DESCRIPTION

Embodiments of the present invention will be described hereinbelow withreference to the accompanying drawings. In the following description,well-known functions or constructions are not described in detailbecause they would obscure the invention in unnecessary detail. For thisapplication, the following terms and definitions shall apply:

The terms “communicate” and “communicating,” as used herein, refer toboth transmitting, or otherwise conveying, data from a source to adestination and delivering data to a communications medium, system,channel, network, device, wire, cable, fiber, circuit, and/or link to beconveyed to a destination.

The term “computer,” as used herein, refers to a programmable devicedesigned to sequentially and automatically carry out a sequence ofarithmetic or logical operations, including without limitation, personalcomputers (e.g., those available from Gateway, Hewlett-Packard, IBM,Sony, Toshiba, Dell, Apple, Cisco, Sun, etc.), handheld, processor-baseddevices, and any other electronic device equipped with a processor ormicroprocessor.

The term “processor,” as used herein, refers to processing devices,apparatus, programs, circuits, components, systems and subsystems,whether implemented in hardware, tangibly embodied software or both, andwhether or not programmable. The term “processor,” as used hereinincludes, but is not limited to, one or more computers, hardwiredcircuits, signal modifying devices and systems, devices and machines forcontrolling systems, central processing units, programmable devices andsystems, field-programmable gate arrays, application-specific integratedcircuits, systems on a chip, systems comprising discrete elements and/orcircuits, state machines, virtual machines and data processors.

The present disclosure endeavors to provide systems and methods forenabling the operation of an autonomous self-charging aerial vehiclesurveillance system. More specifically, the present disclosure endeavorsto provide systems and methods for providing a self-charging UAV and UAVsystem capable of autonomous capture and release for use in a ContinuousOperation System. While utilizing utility power lines for both perchingand inductance charging is possible, a UAV system of the presentinvention preferably utilizes off-site charging through direct currentlines (e.g., via a charging cable 804). An advantage of this approach isthat the charging mechanisms on the UAV may be simplified, thus reducingthe cost and weight of the UAV. Moreover, by using off-site chargingstations equipped with direct current lines, UAVs are not forced to relyon ideal conditions of the power line to facilitate charging (e.g.,current, voltage, diameter, etc.), thus expanding the scope of suitableWaypoint Locations.

For example, as illustrated in FIG. 1, a Continuous Operation System 100may permit continuous, fully autonomous operation of one or more UAVs106 for surveillance purposes. Each UAV 106 may employ one or moresensors to facilitate autonomous flight, including, but not limited to,ultrasonic sensors, infrared sensors, radar and the like. To collectdata and monitor an area, the UAV 106 may be equipped with a traditionalintelligence, surveillance, and reconnaissance (ISR) payload. Forexample, the UAV 106 may be equipped with a payload pod comprising oneor more cameras, audio devices and other sensors. Any video, image,audio, telemetry and/or other sensor data (“Surveillance Data”),collected by the UAV 106 may be locally stored or wirelesslycommunicated from the UAV 106 (e.g., at the Waypoint Location 104 orduring flight) to a Ground Control Station 102 in real time using anantenna coupled with an onboard wireless communication device, such as atransmitter/receiver. Alternatively, Surveillance Data may becommunicated, or otherwise transferred, to the Ground Control Station102 or another party via a wired connection.

In operation, a UAV 106 may alternate between a Waypoint Location 104and a charging location, such as a Ground Control Station 102. The UAV106 should be capable of autonomous landing and takeoff using, forexample, an optical sensing system with an onboard precisionvision-processing computer. At each of the Waypoint Location 104 andGround Control Station 102, the UAV 106 may capture an arresting cable310 to arrest itself and perch. As used herein, the two general types ofarresting cables 310 include perching cables and charging cables 804.Each of the perching cable and the charging cable 804 are capable ofcapturing and supporting a UAV 106 while it perches, however, as will bediscussed in greater detail below, a charging cable 804 provides theadditional function of charging the UAV 106's batteries.

For example, at the Waypoint Location 104, a utility power transmissionline may function as a perching cable. To facilitate targeting whenperching, a predetermined perching point on the perching cable may bemarked using markers, such as IR reflectors. A UAV 106 may be furtherconfigured to autonomously charge itself upon return to the GroundControl Station 102, or other charging stations, through an electrifiedcharging cable 804 on which the UAV 106 may perch and recharge.Accordingly, at the Ground Control Station 102, a charging cable 804 maycomprise two direct current wires carrying power and groundtransmission. As with the Waypoint Location 104, a predeterminedperching point may be marked on the charging cable 804 using markers.

Depending on the operation, the Ground Control Station 102 may bepermanently installed or portable to facilitate on-the-move operations.By employing a plurality of UAVs 106 in a Continuous Operation System100, continuous fully autonomous surveillance is enabled, thus enablingcontinuous surveillance by providing a real time Surveillance Data feedto the Ground Control Station 102 and/or another monitoring facility.

FIG. 2 provides a block diagram for a UAV 106 communicatively coupledwith a Ground Control Station 102 via a wireless data link. Each UAV 106typically includes an onboard processor 108 that controls the variousUAV components and functions. The processor 108 may be communicativelycoupled with an Inertial Navigation System (“INS”) 114 (e.g., Vector NavVN-100) that is communicatively coupled with an inertial measurementunit 116 and GPS receiver, an onboard data storage device 112 (e.g.,hard drive, flash memory, or the like), a surveillance payload 118, oneor more batteries 142, a battery system 130, a wireless communicationdevice 120, or virtually any other desired services 110.

To collect data and monitor an area, the UAV 106 may be equipped with atraditional ISR surveillance payload 118. For example, the UAV 106 maybe equipped with one or more cameras 118 a, audio devices, and/or othersensors 118 b. Any Surveillance Data collected by the UAV 106 may bewirelessly communicated to the Ground Control Station 700 in real timevia the wireless communication device 120. The UAV 106 may be furtherequipped to store said Surveillance Data to an onboard data storagedevice 112. However, if the UAV 106 is operated in an unfriendly zone,it may be advantageous to encrypt all stored data, includingSurveillance Data, or to implement a data self-destruction protocol. TheUAV 106 may be programmed to erase, or otherwise destroy, the onboarddata storage device 112 if the UAV 106 determines that it may havefallen into an enemy's possession. For example, the UAV 106 onboard datastorage device may be erased automatically when communication betweenthe Ground Control Station 102 and UAV 106 is lost or upon touching downin a location outside of a predefined radius from the Ground ControlStation 102 and/or Waypoint Location 104, based on GPS calculations, or,if a crash is detected, e.g., based on detection of a sudden impact.

Data may be communicated between the UAV 106 and Ground Control Station102 via the wireless communication device 120, which is operativelycoupled to the processor 108. For example, the wireless communicationdevice 120 may be configured to communicate data (e.g., SurveillanceData and/or flight control data) with the Ground Control Station 102. Tofacilitate optional wireless communication, the UAV 106 may furthercomprise an air communication link 120 enabled to transmit (“TX”) andreceive (“RX”) data using one or more antennas (e.g., top and bottom)via a circulator 126, LNE 122 and RFE 124. The antenna may be controlledvia the processor 108 that is operatively coupled to an RF switch 128.

In urban environments, multipath interference can become a problem.Thus, standard analog video transmitters and many digital transmissionmethods may not be able to cope with this type of interference.Therefore, to mitigate this problem, the UAV may be equipped with codedorthogonal frequency division multiplexing (“CoFDM”) radios. CoFDM is amodulation format that is highly resistant to multipath interference.Since an operation may call for the UAV 106 to communicate SurveillanceData from a stationary Waypoint Location 104 below a roofline, amultipath resistant radio may be useful by eliminating the need tolaunch and re-land to improve radio reception from a perching point.

The Ground Control Station 102 typically includes a processor 132 thatcontrols the various Ground Control Station 102 components andfunctions. The processor 132 may be communicatively coupled with acommunication transceiver 136, an I/O device 140, a power supply 138 anda charging cable 804. When the UAV 106 is perched on the Ground ControlStation 102's charging cable 804, the UAV 106's battery system 130 iselectrically coupled with the Ground Control Station 102's Power Supply138, thereby charging the UAV 106's one or more onboard batteries 142.As noted above, to reduce weight and cost, it is preferable to directlycouple the battery system 130 with the Ground Control Station 102'sPower Supply 138 via the charging cable 804. However, other methods arepossible, such as inductance charging.

The Ground Control Station 102's communication transceiver 136 may beused to wirelessly communicate data signals with the UAV 106 and/or anend user. Specifically, Surveillance Data collected by the UAV 106 maybe transmitted in real time to the end user for live viewing, or to anapparatus (e.g., a computer) where it may be stored and/or displayed.Similarly, flight control data (i.e., flight commands from the end useror a flight computer) may be communicated between the Ground ControlStation 102 and UAV 106 using the communication transceiver 136.Alternatively, the Ground Control Station 102 may employ separatecommunication transceivers for communicating with the UAV 106 and withan end user. For example, the Ground Control Station 102 may communicatewith an end user through a pre-configured high bandwidth directionaldata link and/or a satellite-based tactical data link. As illustrated,the Ground Control Station 102 may be electronically coupled to a powersupply 138. The power supply 138 may be, for example, a battery, agenerator, line current (e.g., from a power grid), a solar cell, etc.The I/O Device 140 may be coupled with one or more sensors, such as awind gauge 706.

To further enhance data communication, the Ground Control Station 102may be equipped with an enhanced data receiving system. For example, theGround Control Station 102 may be provided with a mechanically steeredantenna system, or a multi-antenna diversity system that can allow muchhigher gain antennas to be used, thereby greatly extending the range ofthe UAV's data link without increasing the power consumption of the UAV106's transmitting radios. With each additional antenna added to thesystem, a higher gain antenna can be utilized. For example, the GroundControl Station 102 may employ a smart antenna (e.g., an adaptive arrayantenna, multiple-antenna and multiple-input and multiple-output)combined with smart signal processing algorithms for (i) identifyingspatial signal signatures such as the direction of arrival (DOA) of thesignal, and (ii) calculating beam-forming vectors to track and locatethe antenna beam on the mobile/target.

While multiple identical UAVs 106 are illustrated in FIG. 1, aContinuous Operation System 100 may employ a plurality of UAVs 106 ofdifferent types and sizes. Indeed, specially equipped UAVs 106 may bedeployed to a particular Waypoint Location 104 to meet a specific need.However, compact lightweight UAVs are generally advantageous as theyyield minimal detection and reduce weight imposed on the arresting cable310. Indeed, as will be shown below, a suitable UAV 106 that may bemodified to facilitate Continuous Operation System operations includesthe back-packable Skate™ UAS, available from Aurora Flight Sciences.

The Skate™ system is able to fly with its ISR payload, The Skate™ systemcan carry out autonomous missions from takeoff to landing without pilotintervention, but it is not able to land and take off again withoutassistance. The Skate™ system uses independently articulating thrustvectoring motor pods to allow rapid transition between vertical andhorizontal flight. Transitioning from vertical take-off and landing(VTOL) to wing-borne flight increases the endurance and range of thesystem to levels characteristic of a fixed-wing platform and far beyondthose of a traditional VTOL asset. The thrust vectoring provided by themotor pods allows the Skate™ UAV to fly both vertically and horizontallyindoors and out, enabling rapid navigation of cluttered environmentssuch as city streets or building interiors. For additional informationregarding the Skate™ system, see Aurora Flight Science's website andcommonly owned U.S. Pat. No. 8,721,383 (filed Sep. 9, 2009) and U.S.Pat. No. 8,500,067 (filed Aug. 4, 2012), which are each entitled“Modular Miniature Unmanned Aircraft With Vectored-Thrust Control.”

While the present invention illustrates a modified Skate™ UAV in theContinuous Operation System 100, one of skill in the art wouldappreciate that the present invention should not be limited to use withthe Skate™-type UAVs. On the contrary, virtually any small UAV or SUASmay be modified to meet the objectives of a Continuous Operation System100. Such features including, for example, unattended recharging,autonomous cable capture and launch, and video-based flight controlsthat permit accurate perching point targeting, as well as the extendedendurance to a one hour mission with a half-pound payload. However, amodified Skate™ UAV is illustrated in the following examples because ofits advantageous airframe characteristics. Moreover, the Skate™ UAV maybe equipped with an autopilot capable of flying to waypoints (e.g., aWaypoint Location 104) and performing many fully autonomous missionsthrough a full suite of sensors including, for example, GPS, barometricpressure for altitude, differential pressure (e.g., a Pitot tube) forairspeed, and a full 9-DOF inertial measurement unit.

The existing Skate™ UAS configuration represents a balance of the needfor vertical launch/recovery, with the desire for persistent presence,and the physical constraints imposed by back packability (e.g., theability to carry the UAV in a backpack). Therefore, the resulting Skate™planform compromises by providing an aspect ratio selection driven bymaneuvering and payload constraints, as opposed to an optimized cruisecase, and wingspan limited by packaging requirements. This low aspectratio planform provides a wide angle of attack envelope, facilitatinginbound perch transition and controlled steep glide slopes forlanding/maneuvering in confined spaces, but increasing induced drag atcruise. However, relaxing the aspect ratio constraint, by incrementallyincreasing wingspan, can improve cruise performance with minimal impacton maneuvering and storage capabilities. Therefore, because backpackability is not necessarily required in a Continuous Operation System100, lengthening the wingspan of the UAV 106 can both increase theaspect ratio and reduce the wing loading, translating directly to lowercruise power requirements.

Indeed, as illustrated in FIG. 3a , a Skate™ UAV may be modified using,for example, 3-inch wingtip extension 302 on each wing. By implementingwingtip extensions 302, changes to the Skate™ UAV'smechanical/propulsion systems are not required. To account for theincrease in wingspan, the vertical stabilizers 304 may also be enlarged,or raked, to meet new tail volume requirements. To enable perching on anarresting cable 310, any sub fins may be eliminated from the undersideof the UAV 106 thereby avoiding interference with any landing/capturedevices, including arresting devices 306.

The UAV 106 should also be configured to capture onto, or otherwiseengage, an arresting cable 310 using one or more arresting devices 306located on the underside of the UAV 106. During and after the arrestingoperation, the UAV 106 may be configured to swing down and hang invertedfrom the arresting cable 310 to execute its surveillance objectives asillustrated in FIG. 3b . Providing the arresting devices 306 on theunderside of the UAV 106 allows for increased clearance between theoncoming arresting cable 310 and the propellers 312, but also allows forexcellent ground visibility from the surveillance payload pod 308.Accordingly, a UAV 106's ISR payload pod 308 may be preferably locatedon the top of the UAV 106 (e.g., opposite the arresting device 306).Therefore, when the UAV 106 is hanging inverted, the payload pod 308faces downward, and provides the opportunity to mount a gimbaled camera,or other sensors, with a full 360-degree view of the ground. Thisorientation also maximizes exposure of the payload pod 308 with theground where, from this position, the UAV 106 will be able to observeany ground location below the arresting cable 310.

To facilitate surveillance functionality, the UAV may wirelesslytransmit Surveillance Data back to the Ground Control Station 102. Fromthere, the data may be relayed to end users (e.g., remote operators)either through a pre-configured high bandwidth directional data link orthrough a satellite-based tactical data link. Alternatively, the UAV maywirelessly transmit any data directly to the remote operators.

To facilitate capture (landing) and release (takeoff), thecable-arresting mechanical system, which may comprise one or morearresting devices 306, may be designed to release the UAV 106 either oncommand (i.e., actively) or when the UAV 106 generates enough thrust tolift off the arresting cable 310 (i.e., passively). For example, the UAV106 may power its motors to reaches a stable condition wherein thevehicle is pointed nearly vertically (e.g., perpendicular to the ground)and is pulling against the arresting cable 310. At this point, theautopilot simultaneously applies increased power to the motors andactuates the servo releasing the one or more arresting devices 306'shook from the arresting cable 310. Thus, the UAV 106 releases from thearresting cable 310 and launches vertically to a predetermined altitudebefore resuming level flight and navigation to a waypoint location(e.g., Ground Control Station 102 and/or Waypoint Location 104). Beforethe takeoff sequence, the UAV 106 hangs inverted, but since thepropellers 312 are offset from the arresting devices, rotating back tovertical is not a difficult operation.

To facilitate capture and release of the arresting cable 310, the UAV'sflight control system may be provided with camera-derived estimates ofthe target arresting cable 310's relative azimuth, elevation, and range.Together with the state estimate of the vehicle itself, this informationis sufficient to determine line-of-sight rate and range rate to thetarget, which in turn can be used to implement a homing algorithm suchas pure pursuit, proportional navigation (PN), or variations on PN thatreduce the reliance on range rate information (which may be of loweraccuracy in windy situations). For example, in operation, the UAV mayguide itself to the desired landing site using GPS, along the approachheading designated by the installation crew. Once the UAV comes within apredetermined distance of the landing zone (e.g., about 20-30 feet fromthe perch point) the UAV can activate the sensing system. The UAV maydetect the cable markers (e.g., IR illuminators and/or IR reflectors)and may utilize a terminal guidance algorithm to impact the arrestingcable 310 at a slower cruise. In the event that the sensing system doesnot detect the markers, or the UAV encounters a wind gust and misses thearresting cable 310, the UAV can perform an abort operation. An abortoperation may comprise, for example, climbing rapidly aboveobstructions. Since the UAV may be capable of a vertical takeoff, theUAV can rapidly ascend to a safe altitude and fly around for anotherattempt.

The UAV 106 may employ an onboard vision processing system capable ofperforming real time centroiding on the incoming video and calculatingrelative altitude estimates. This may be done at a conservative minimumof 30 frames per second (fps), although 60 fps may be preferable. Forexample, an OMAP™ 3-based cellular phone processor may be used toprovide a vision processing system because it is highly miniaturized anddesigned for low power operation. The perch point cable markers may beplaced on an arresting cable 310 and may be detected using, for example,IR beacons, coupled with the onboard vision processing system. Thismethod is advantageous because IR light can be effectively utilized inboth day and night with proper selection of IR frequency (e.g., 940 nm).Since centroiding generates sub-pixel resolution accuracy, high pixelcamera resolution may not be necessary to achieve high accuracy results.Consequently, the primary metrics for selection of the camera may besize, weight and ease of integration. For example, a suitable camera maybe a miniature camera based on an Aptina monochrome image sensor.Testing of the marker performance is analyzed through an RGB intensitygraph.

Accordingly, as illustrated in FIG. 8, arresting cables 310, whethercharging or perching cables, may be marked with a marker 812, such asactive IR illuminator (e.g., Phoenix Jr. Infrared Beacons) and/or IRreflectors (e.g., retro-reflective tape), which functions in IR (e.g.,“Glint Tape” that is available from U.S. Tactical Supply; Emdomretro-reflective ID Marker; 3M 3000X or 3M 7610 Reflective Tape; oranother all-purpose adhesive light strips). The IR illuminator has theadvantage of not requiring an IR light source on the UAV, but wouldrequire power of some kind (e.g., onboard batteries.) Conversely, the IRreflectors, which are passive, would require an illuminator on the UAV.

For example, two markers may be attached to the arresting cable 310 toenable the vehicle to easily detect relative bank angle compared to thecable, relative pitch and heading as well as to estimate a roughdistance to target. The onboard vision processing can centroid theincoming images, and determines the centers of the IR beacons in thefield of view. To identify a perching point, the vision processingsystem can input these centroid coordinates and calculate the relativealtitude estimates to feed into the landing control system.

FIGS. 4a through 4d illustrate an example cable capture and releasemaneuver. In FIG. 4a , once the perching point has been located, the UAV106 approaches the arresting cable 310, whether a perching cable orcharging cable 804, at cruise speed with the arresting devices 306lowered. The UAV 106 may be equipped with one or more retractablearresting devices 306 on the underside of the UAV 106. The distal end ofeach arresting device 306 may be provided with a capturing hook 314(e.g., a capture and release mechanism), such as the passively lockingjaw illustrated in FIGS. 5a and 5b . Moreover, to increase lateralstability, it is preferable to capture the arresting cable 310 at two ormore points, which may be accomplished by employing two arrestingdevices 306 or a single apparatus having two or more capturing hooks314.

With the arresting device 306 hanging below the UAV 106, aircraftcomponents (e.g., the propeller, ISR pod and tails) do not pose asnagging risk with the arresting cable 310, and an abort maneuver can beperformed simply by pitching up and away from the arresting cable 310.As illustrated in FIG. 4b , the arresting device 306 may strike thearresting cable 310 and capture it via the one or more capturing hooks314. The arresting device 306 may be configured such that an arrestingcable 310 may strike at any point along the shank 510 and result in acapture. Once locked, the UAV 106 swings forward and/or down to hangbelow the arresting cable 310. To increase strength, the arrestingdevice 306 may be secured to the UAV's main structure (e.g., the payloadpod 308's attachment brackets) thus transferring arresting loads (e.g.,energy) into the main structure of the airframe. Once the UAV 106 ishanging below the arresting cable 310, the payload 308 has anunobstructed view of the surroundings.

After charging, or surveying an area of interest, the UAV 106 is readyto re-launch. By throttling up the motors to a thrust-weight setting, asillustrated in FIG. 4c , the UAV 106 will rotate around the arrestingcable 310 and be pulled into a vertical launch position. At this point,the arresting device 306 will release. By omitting sub-fins, the portionof the airframe behind the arresting device 306 is obstruction free. Asillustrated in FIG. 4d , the UAV 106 climbs up and away from thearresting cable 310, transitioning back to a cruise altitude. Thearresting device 306 may then retract into the fuselage of the UAV 106to reduce drag.

FIGS. 5a and 5b provide an enlarged view of an example arresting device306 while FIGS. 6a through 6d provide enlarged views of the arrestingdevice 306's capturing hook 314 during the cable capture and releasemaneuver of FIGS. 4a through 4d . As illustrated, the capturing hook 314for engaging an arresting cable 310 during capture and release of anaerial vehicle generally comprises a first gate 502 pivotally supportedat a first end by a base portion of the shank 510 and movable between(i) a closed position (e.g., FIGS. 6a and 6c-6e ) and (ii) an openposition (e.g., FIG. 6b ) and a second gate 504 pivotally supported at afirst end by the base portion of the shank 510 and movable between (i) aclosed position and (e.g., FIGS. 6a-6d ) (ii) an open position (e.g.,FIG. 6e ). To prevent the first gate 502 from inadvertently opening, afirst return spring 516 biases the first gate 502 in the closedposition. Similarly, to prevent the second gate 504 from inadvertentlyopening, a latch device 514 comprising a movable locking part 506 biasedby a return spring 518 to a locked position to lock the second gate 504in the closed position. When the first gate 502 and the second gate 504are both in the closed position, the first gate 502 may be configuredsuch that the first gate 502's second end 520 slips within a recess 522at the second end of the second gate 504, thereby preventing thearresting cable 310 from inadvertently slipping out of the hook recess512.

More specifically, FIG. 6a illustrates the arresting device 306'scapturing hook 314, which is a passively locking jaw resembling a clevistype hook, in a lowered position as the UAV 106 approaches an arrestingcable 310 (e.g., a charging cable 804 comprising a wire pair) at cruisespeed. FIG. 6b illustrates the capturing hook 314 in the course ofcatching the arresting cable 310. In operation, the arresting cable 310may either (i) make direct contact with the capturing hook 314's firstgate 502, or (ii) pass along the arresting device 306's shank 510 untilit reaches the capturing hook 314's first gate 502. Regardless of theinitial contact, once the arresting cable 310 makes contact with thefirst gate 502, the force of the arresting cable 310 can cause the firstgate 502 to push backward in direction C about pivot point Y, thusproviding access to the capturing hook 314's hook recess 512. Once thearresting cable 310 is in the hook recess 512 of the capturing hook 314,a force (e.g., an extension spring) may cause the first gate 502 to snapback in direction C, as illustrated in FIG. 6c , thereby securing thearresting cable 310 in the hook recess 512.

FIG. 6d illustrates the capturing hook 314 prior to releasing thearresting cable 310. While perched and during the takeoff maneuver, thearresting cable 310 generates a force against the second gate 504 indirection A. To release the arresting cable 310 from the hook recess512, a servo-controlled release wire may be configured related to thelatch device 514 by pulling the a movable locking part 506 in directionB about pivot point Z, thus enabling the second gate 504 to open bypivoting about pivot point X as illustrated in FIG. 6d . As illustratedin FIG. 6e , the lift and thrust of the UAV 106 applies a tension to thearresting cable 310 during takeoff that pulls the second gate 504 openthereby releasing the UAV 106 to facilitate free flight, as shown inFIGS. 4c and 4d . Once released, the force from the arresting cable 310pulling on the second gate 504 is gone and an extension spring pulls thesecond gate 504 back into its closed position and allows the latchdevice 514 to lock it in place, ready for the next capture. Thearresting device 306's design eliminates the need for a controls/sensingintensive dynamic perch maneuver. By approaching the arresting cable 310at or near cruise speed, the UAV 310 can be much less susceptible togusts, and the controls approach can be greatly simplified (i.e. not inthe post-stall regime). The arresting device 306's design enables theContinuous Operation System 100.

As illustrated in FIG. 7, a Ground Control Station 102 may be positionedon a rooftop, or other substantially clear area (e.g., clear fromlanding/takeoff obstruction) near the area of surveillance. Once aGround Control Station 102 has been configured, a Waypoint Location 104having an arresting cable 310 (e.g., power, telephone orspecially-installed cable) for the UAV 106 may be identified or created.Since the arresting cable 310 may be pre-surveyed, an operator candesignate an approach direction; the GPS coordinate location and/oraltitude of the perching zone (e.g., the area immediately surroundingthe arresting cable 310). The arresting cable 310 may also be marked orequipped with markers, such as IR beacons, that allow the UAV 106 tolocate the arresting cable 310 using its onboard sensory system. Aftersurveying and marking an arresting cable 310 within a perching zone, theUAV may approach and land on the arresting cable 310.

Since the UAV 106's operation is autonomous, the UAV 106 may beconfigured to launch from a Ground Control Station 102, fly a mission(e.g., perch at a Waypoint Location 104), then return to the GroundControl Station 102 to charge itself in preparation for the nextautonomous launch. To facilitate this functionality, a Ground ControlStation 102 may provide a charging cable 804 for electrically connectingto the UAV 106 to facilitate charging after the UAV 106 has perched onthe charging cable 804. A diagram of an example Ground Control Station102 is illustrated in FIG. 7.

To facilitate autonomous takeoff and capture (landing), a Ground ControlStation 102 may comprise a charging cable 804, a communicationstransceiver 136 and wind gauge 704. The charging cable 804 may besupported by one or more dedicated posts 708. Accordingly, the GroundControl Station 102 may be configured to be self-supporting so that itmay stand on its own in an open field. Alternatively, the charging cable804 may be coupled with independent structures, such as buildings,telephone poles, etc. In fact, the entire Ground Control Station 102 maybe coupled with, or integrated with, a vehicle to provide a mobileGround Control Station 102 where the UAV 106 can locate the GroundControl Station 102 via the wireless antenna and/or GPS tracking.Similarly, the wind gauge 704 may be integrated with the Ground ControlStation 102 via an I/O device 140 to provide wind data (e.g., speed anddirection) or remotely located wherein the wind data is communicated tothe Ground Control Station 102 via communications transceiver 136.Regardless of the configuration, to account for landing and takeoffmaneuvers, the charging cable 804 should be designed and positionedsufficiently off the ground to provide an adequate amount of landinglength for the UAV. For example, the charging cable 804 length may be 15feet and positioned substantially parallel to the ground at a height of15 feet.

A notable feature of the charging cable 804 is that it may directlyelectrically interface with the capturing hook 314 to facilitatecharging the UAV 106's battery while perched on (e.g., hanging from) thecharging cable 804. Specifically, the charging cable 804 preferablycomprises conductive wires (e.g., ground and power) that interface withthe UAV 106's battery system via the capturing hook 314. In doing so,the conductive wires should be configured to minimize the risk ofshorting (e.g., making contact with each other) directly, or throughsome part of the UAV 106's hook, once the UAV has perched and is hangingin steady state.

A cable management system for use in Ground Control Station 102according to the present invention may be illustrated by the followingexample. This example is provided to aid in the understanding of theinvention and is not to be construed as a limitation thereof. Asillustrated in FIG. 8, two extendable (e.g., telescoping) poles 802 maybe spaced apart and extended into the air. For a small UAV 106, thepoles 802 may be spaced 15 feet apart and extend 15 feet into the air.To tether the poles 802 to the ground, a first end of two or moreguy-lines 804 may be coupled to the top of each pole 802 via one or moremounts while a second end may be coupled to one or more groundattachment points 806 (e.g., ground stakes). While the guy-lines 804 maybe constructed from rope, cable may be employed to reduce anydisplacement resulting from guy-line stretching. The mount for theguy-lines may be configured such that each guy-line may attach to itsown mount with some distance between them, thus adding moment resistanceto the setup, thereby reducing twisting of the poles 802. Moreover,ratcheting tensioning devices may be provided in line with the guy-lineto facilitate larger adjustments while turnbuckles may be provided tofacilitate fine adjustments.

A charging cable 804 may be stretched between the poles 808 to captureand charge a UAV 106. The charging cable 804 may be further threadedthrough one or more pulleys 808 and coupled to one or more cablemanagement devices 810. Each cable management device 810 may beconfigured to provide a constant charging cable 804 tension augmented bya shock absorber to absorb energy during UAV capture. Indeed, thecharging cable 804 should be configured as to provide a soft catch tothe UAV 106, thereby minimizing the risk of damage after repeated use.Example cable management devices 810 may include, for example, a winchcoupled with one or more shock absorbers, springs (linear or torsional),elastic cables, or hydraulics. To increase reliability, the cables maybe kept on the pulleys with cable guards or routed through cablehousings.

While the following example is applied to a charging cable 804, the samefunctionality may be used in conjunction with any perch point, such asan arresting cable 310 positioned at a Waypoint Location 104. Forexample, as discussed above, the charging cable 804 may be marked withtwo or more markers 812, such as active IR beacon and/orretro-reflective tape. The markers 812 may be attached to the chargingcable 804 to enable the UAV 106 to detect relative bank angle comparedto the charging cable 804, relative pitch and heading as well as toestimate a rough distance to target. The UAV 106's onboard vision basednavigation system can centroid the incoming images to determine thecenters of the IR beacons in the field of view, thereby identifying thecharging cable 804. The vision navigation algorithm is continuallytrying to identify a target. When a possible target is recognized, aninternal counter verifies that it has been continually identified forseveral frames. Upon recognition of the beacons, a signal is sent to theouter-loop controller and the vehicle guidance is switched into avision-based tracking routine. Specifically, heading and altitudecommands may track the location of the target to the center of the fieldof view. The target was set as the central markers, detected by thevision based navigation system algorithms where offsets in the lateraldirection commands heading, and vertical offset commands altitude.Accordingly, a low level altitude and heading tracker was implemented inthe autopilot.

Accordingly, the general objective of a vision based navigation systemis to determine the estimation and control approach for a UAV 106 flyingtowards an identified visual source and using the information of theobserved location of two or more known markers 812 in the camera frameto reach a specific location (e.g., a Ground Control Station 102 orWaypoint Location 104). Measurements available to the vision basednavigation system may include, for example, position data from a GPSdevice, attitude with respect to a global reference frame (e.g., usingVectorNav) and the location of predetermined points in the camera frame(e.g., using Sanford image processing). Markers 812 or other beaconpoints may be located in the environment and the MAV may be providedwith data regarding the markers 812's location with respect to thecharging cable 804. For example, the specific location should bevisually accessible to the camera at least up to a point where the UAV300 may achieve a final approach with increased certainly. That is, asthe UAV 300 gets closer to the specific location, the markers 812 shouldfall within the field of view of the camera up to a very short distanceto the target location. The markers 812 are known, or assumed, to belocated at some predetermined points on the cable.

FIG. 9a illustrates a block diagram of an example vision basednavigation system 900. As illustrated, the vision based navigationsystem 900 may comprise one or more image capture devices 902, a pointcorrelation device 904, a thresholding device 906, a feature trackingdevice 908, a likelihood filter 910, and a Kalman estimate device 912.

The one or more image capture devices 902 may be configured to receive,or generate, an image of an area. The one or more image capture devices902 may include, for example, an onboard camera. The image of the areamay be a still photo or a video, which generally comprises a series ofstill photos known as frames. The thresholding device 906 may beconfigured to determine the location of features within the image. Forexample, markers 812 may be used to provide image points with highintensity levels that can be extracted from the image by thresholding.Accordingly, the information from the image capture devices 902 (e.g.,camera) can provide the coordinates (u,v) for points within acorresponding threshold. For example, a detected light that exceeds apredetermined threshold intensity value may be represented as acoordinate within the image. The feature tracking device 908 may employa feature tracking algorithm, such as Lukas-Kanade, to calculate themotion of the image locally using the coordinates by tracking the motionof a feature (e.g., a coordinate) from frame to frame. This processallows for filtering out coordinates that do not correspond to themarkers 812 as they are tracked. However, additional calculations mayfurther be employed to track of the markers, or other features.Specifically, an algorithm may track features over different frames butmay not identify which ones are the markers.

The point correlation device 904 and likelihood filter 908 may be usedto reduce the coordinates by eliminating outlier coordinates based on,for example, a linear correlation. Since the locations of the markers istypically known (e.g., on a power line), the markers should meet a knowngeometric constraint. Accordingly, a first approach may be to assumethat a valid set of points should lie on a line (or close to it) asshown in FIG. 9b . Therefore for vision based navigation system 900selected n-sets of points, the likelihood filter 908 can determinewhether the points are within a threshold of being in a line by checkingthe error from a linear fit. From here, there are two possibleapproaches to beacon detection: one based on closed-loop, time-varyingthresholding and a Kalman Filter-based approach. The Kalman estimatedevice 912 comprises a Kalman filter, which uses input from GPS, the IMUand the Camera to produce the best estimate of the position and/orattitude with respect to the markers. Generally speaking, a Kalmanfilter is an algorithm that uses a series of measurements observed overtime, containing noise (random variations) and other inaccuracies, andproduces estimates of unknown variables. Moreover, the routine mayidentify features that are consistent over time in spite of thetime-varying brightness threshold to eliminate noise and reflectionsthat are less consistent in brightness over time. A standard ExtendedKalman Filter approach is used to predict the state and update thecovariance:{circumflex over (x)} _(k|k−1) =f({circumflex over (x)} ⁺ _(k−1|k−1) ,u_(k−1))P _(k|k−1) =F _(k−1) P _(k−1|k−1) F _(k−1) ^(T) +Q _(k)

To filter out sources of noise, reflections, and non-beacon lights, aclosed-loop thresholding algorithm may be used to alters the brightnessthreshold in real-time to select a subset of points (e.g., 5 or so). Theclosed-loop thresholding algorithm may work in conjunction with thelikelihood filter that may have more time-varying brightness levels thanthe beacons themselves.

FIG. 9b illustrates an example process of analyzing an image using avision based navigation system 900. At step 1, the vision basednavigation system 900 generates, or otherwise receives, an image of agiven area. The area may be the view of the UAV 300 during flight (e.g.,akin to the view from a manned aircraft's cockpit). The cameraparameters may be assumed, such as focal length and cameraconfiguration.

At step 2, a series of coordinates are identified based on the imageusing thresholding techniques. Specifically, the various light sourcesdetected in the image are represented using one or more coordinates on acoordinate plane. The light sources are represented on the plane whenthey exceed a predetermined threshold intensity value. As illustrated,in addition to the two markers, the various street lamps also exceed thethreshold intensity and thus are similarly represented on the coordinateplane. Using intense beacons will provide image points with highintensity levels that can be extracted from the image by thresholding.The information from the camera will provide the (u,v) coordinates forpoints within a corresponding threshold. The measurement model used isthe standard pinhole model:

$u = \frac{X_{f}}{Z}$ $v = \frac{Y_{f}}{Z}$

a convenient way used to express this model is:

$p = {{\lambda\begin{pmatrix}u \\v \\1\end{pmatrix}} = {{\begin{pmatrix}f & \tau & o_{x} \\0 & {\eta\; f} & o_{y} \\0 & 0 & 1\end{pmatrix}\begin{pmatrix}X_{cam} \\Y_{cam} \\Z_{cam}\end{pmatrix}} = {KX}_{cam}}}$

Where τ, η, o_(x), o_(y) are parameters of the camera describingdistortion and offset. As mentioned in the assumptions, τ, η, will beconsidered 0, 1 (no shear or compression distortion). The location of apoint p_(A) in the camera frame can then be calculated as:λp _(A) =KR(−X+x _(A))  (1)with:λ=R ₃(−X+x _(A))  (2)

Where

$R = \begin{bmatrix}R_{1} \\R_{2} \\R_{3}\end{bmatrix}$is the rotation matrix from the absolute frame to the camera frame:R=R_(cam/body)R_(body/X)

Where, X is the coordinates of the camera with respect to the targetlocation, and x_(A) is the location of the beacon with respect to thetarget location. The gradient of the measurement equation H can becalculated by implicit differentiation of equations (1) and (2) to be:

$\begin{matrix}{H_{k\_ p} = {\left. \frac{\partial p_{A}}{\partial X} \right|_{{\hat{x}}_{k}} = \left. {{- \frac{1}{\lambda}}\left( {{KR} + {p_{A}R_{3}^{T}}} \right)} \right|_{{\hat{x}}_{k}}}} & (3)\end{matrix}$

At step 3, a RANdom SAmple Consensus (RANSAC) algorithm may sampledifferent combinations of n-points. At step 4, the coordinates arereduced by eliminating outlier coordinates based on a known geometricconstraint, for example, a linear correlation. That is, outliers thatcorrespond to 3D points reflecting or emitting IR that may not bediscerned from the correct beacons to be tracked. Thus, a preliminaryfilter that can reduce the data points by rejecting outliers is based ona linear correlation. Since the beacons are known to be located on apower line, they should meet a specific geometric constraint. As a firstapproach we will assume that a valid set of points should lie on a line(or close to it). Therefore for every selected pair of points we cancheck if they are within a threshold of being in a line by checking theerror from a linear fit. After the image processing, we have a set ofpoints:P_(k): {p_(k1),p_(k2),p_(k3),p_(k4),p_(k5), . . . }

Which we can group into sets that represents mutually exclusive events:Z_(k): {z_(k) ₁ ,z_(k) ₂ ,z_(k) ₃ ,z_(k) ₄ ,z_(k) ₅ , . . . }

That is:

$z_{k} = {\begin{bmatrix}{\hat{p}}_{A} \\{\hat{p}}_{B} \\{\hat{p}}_{C}\end{bmatrix}_{k} = {\begin{bmatrix}p_{k\; 1} \\{\hat{p}}_{k\; 2} \\{\hat{p}}_{k\; 3}\end{bmatrix}\mspace{14mu}{{or}\mspace{14mu}\begin{bmatrix}p_{k\; 2} \\{\hat{p}}_{k\; 1} \\{\hat{p}}_{k\; 3}\end{bmatrix}}\mspace{14mu}{{or}\mspace{14mu}\begin{bmatrix}p_{k\; 1} \\{\hat{p}}_{k\; 2} \\{\hat{p}}_{k\; 4}\end{bmatrix}}\mspace{14mu}{{or}\mspace{14mu}\begin{bmatrix}p_{k\; 1} \\{\hat{p}}_{k\; 4} \\{\hat{p}}_{k\; 2}\end{bmatrix}}\mspace{14mu}\ldots}}$

Finally, at step 5, the markers, indicated in the figure using a dottedcircle, are identified using likelihood filtering and/or Kalman filter.Indeed, a standard Extended Kalman Filter approach may be used topredict the state and update the covariance:{circumflex over (x)} _(k|k−1) =f({circumflex over (x)} ⁺ _(k−1|k−1) ,u_(k−1))P _(k|k−1) =F _(k−1) P _(k−1|k−1) F _(k−1) ^(T) +Q _(k)

Each point z_(k) indicates a combinatorial of feature points, whichindicate mutually exclusive events. Therefore, we are interested inselecting one of the possible events as the correct one. This may beaccomplished by selecting the one with the largest likelihood asmeasured by the innovation vector and its covariance. After performingthe state prediction, we can look for the event z_(k) _(n) thatmaximizes the likelihood by projecting the innovation of each event(variation from predicted state) in its probability space, and findingdistance to the origin (maximum likelihood). This is equivalent tofinding the event n that minimizes:e_(k) _(n) ={tilde over (y)}_(k) _(n) ^(T)S_(k) ⁻¹{tilde over (y)}_(k)_(n)

With:{tilde over (y)} _(k) _(n) =(z _(k) _(n) −h({circumflex over (x)}_(k|k−1)))S _(k) =H _(k) P _(k|k−1) H _(k) ^(T) +R _(k)

After selecting the measurement with highest likelihood, the filtereddata point is used in the update of the Kalman State estimate:K_(k)=p_(k|k−1)H_(k) ^(T)S_(k) ⁻¹{circumflex over (x)} _(k|k) ={circumflex over (x)} _(k|k) +K _(k){tilde over (y)} _(k) _(n)P _(k|k)=(I−K _(k) H _(k))P _(k|k−1)

One the markers are identified, the UAV 300 may navigate to thearresting cable 310's perch point using an onboard autopilot. Forexample, a terminal guidance control approach may be employed. Usingthis approach, assumptions may be used to reduce the complexity of anapproach. Specifically, one assumption may be that the UAV 300 caninitially identify the beacons on the camera plane, that is, the pointsin the image that correspond to the beacons are known. Additionally,given the ambiguity of the measurements we have to make some assumptionsof states that will be controlled through internal loops.

The beacons may also be tracked from image to image by finding the setthat maximizes the probability of being the same beacon from theprevious frame by calculating the set that minimizes:e=dp^(T)R⁻¹dp

Where dp=(du,dv) is an array of the difference in the measured positionsbetween the identified beacons in one frame, and the detected points inthe next one, R is the covariance matrix of the measurements. Using thatinformation, a line in the image may be defined by two points. Ingeneral, the information from the camera in FIG. 11 may be used, whichillustrates the geometry of the guidance elements in the camera frame.The guidance elements are:

$\alpha = {{atan}\left( \frac{v_{2} - v_{1}}{u_{2} - u_{1}} \right)}$$\beta = {{atan}\left( \frac{v_{2} + v_{1}}{u_{2} + u_{1}} \right)}$γ = β − α e_(θ) = ecos  γ − esin  γ e_(ψ) = esin  γ + ecos  γ${e} = {\frac{1}{2}\sqrt{\left( {u_{2} + u_{1}} \right)^{2} + \left( {v_{1} + v_{2}} \right)^{2}}}$

Where p_(i)=[u_(i), v_(i)], i∈(1,2), is the location of the line extremepoints on the camera frame. The control transfer functions K(s) can be aset of static gains or a dynamic transfer functions set to compensatethe dynamics of the non-linear input to output system.

A first approach may be a constant pitch angle approach. To perform thisapproach it may be assumed that an internal loop tries to maintain aconstant pitch angle, the altitude variations are small, and thealtitude is regulated using thrust. Thus, in general, Pitch angle isconstant. Small variations with respect to the level direction.(Defining level direction as vector from camera to target point isaligned). Under the constant pitch angle assumption we can define aninput-output system:

$\begin{bmatrix}e_{\theta} \\e_{\psi} \\\alpha\end{bmatrix} = {G\begin{pmatrix}h \\\psi \\\phi\end{pmatrix}}$

Control approach will then be based on trying to regulate the altitude,heading and roll based on the observed line (defined by the extremepoints) in the image.

$\begin{bmatrix}\overset{.}{h} \\\overset{.}{\phi}\end{bmatrix} = {\begin{bmatrix}{K_{h\;\theta}(s)} & 0 & 0 \\0 & {K_{\psi\alpha}(s)} & {K_{\phi\alpha}(s)}\end{bmatrix}\begin{bmatrix}e_{\theta} \\e_{\psi} \\\alpha\end{bmatrix}}$

Where θ, ψ, ρ are pitch yaw and roll angles respectively.

A second approach may be control of velocity vector. An objective of thecontrol law is to maintain the camera vector aligned with the finaltarget point, given the assumption that the camera vector is alignedwith the velocity direction, the trajectory converges to the target.

$\begin{bmatrix}e_{\theta} \\e_{\psi} \\\alpha\end{bmatrix} = {G\begin{pmatrix}h \\\psi \\\phi\end{pmatrix}}$

The velocity of the vehicle is aligned with the camera vector. This canbe performed by providing inner control loops that regulate the thrustto achieve such behavior.

$\begin{bmatrix}\overset{.}{\theta} \\\overset{.}{\psi} \\\overset{.}{\phi}\end{bmatrix} = {\begin{bmatrix}{K_{\theta 1}(s)} & {K_{\theta 2}(s)} & 0 \\{K_{\psi 1}(s)} & {K_{\psi 1}(s)} & 0 \\{K_{\phi 1}(s)} & 0 & {K_{\phi 2}(s)}\end{bmatrix}\begin{bmatrix}e_{\theta} \\e_{\psi} \\\alpha\end{bmatrix}}$

Where θ, ψ, ρ are pitch yaw and roll angles respectively.

A third approach may be glideslope. This approach considers a glideslopedefined by an estimated distance to the target from the size of the linein the camera plane and assumes that the pitch angle is held constant.

$h = {1 - \frac{\left( {{p_{2} - p_{1}}} \right)}{Y_{\max}}}$

Inner loops may be employed to achieve the glideslope.

FIG. 10a illustrates a cross sectional diagram of an example chargingcable 804 comprising two conductive wires 1002 separated by annon-conductive insulator 1004, which resembles a twin lead RF cable. Toreduce the risk of shorting the circuit, the arresting device 306 andcapturing hook 314 may be fabricated from a non-conductive materialequipped with conductive contacts 1006 positioned in the hook recess 510of the capturing hook 314 to facilitate an effective electrical contactbetween the UAV 106's battery charging system and the wire conductors1002. An example non-conductive material includes synthetic polymers,such as plastic. To increase conductivity and prevent corrosion, theconductive contacts 1006 may be fabricated from a non-corrosiveconductor, such as gold. Providing wider conductive contacts 1006 allowsfor a large amount of angular movement of the UAV 106 on the cable whilemaintaining electrical contact.

FIG. 10b illustrates an example configuration for positioning conductivecontacts 1006 on the arresting device 306's capturing hook 314 of FIGS.6a through 6e . For example, a first conductive contact 1006 may beplaced on the second gate 504, and a second conductive contact 1006 maybe placed on the base portion of the shank 510. Specifically, the firstand second conductive contacts 1006 should be placed at or near thepoint where the second gate 504 meets the base portion of the shank 510,such that each of the arresting cable 310's conductive wires 1002 may beelectronically coupled with its respective conductive contact 1006. Toaccount for conductive contact 1006 placement, the non-conductiveinsulator 1004's width may be increased or decreased to ensuresufficient contact between each conductive wire 1002 and an associatedconductive contact 1006.

Although the present invention has been described with respect to whatare currently considered to be the preferred embodiments, the inventionis not limited to the disclosed embodiments. To the contrary, theinvention is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims. The scope of the following claims is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures and functions.

All U.S. and foreign patent documents, articles, brochures and otherpublished documents discussed above are hereby incorporated by referenceinto the Detailed Description of the Preferred Embodiment.

What is claimed is:
 1. An aerial vehicle having a vision-basednavigation system for capturing an arresting cable situated at a landingsite, the aerial vehicle comprising: a fuselage having a propulsionsystem; an arresting device coupled to the fuselage, the arrestingdevice to capture said arresting cable at the landing site; a camerasituated on the aerial vehicle; an infrared illuminator situated on theaerial vehicle to illuminate the landing site, wherein said arrestingcable has two infrared reflectors situated on said arresting cable; andan onboard processor to (i) generate a plurality of coordinatesrepresenting features of the landing site using an image thresholdingtechnique, (ii) eliminate one or more coordinates as outlier coordinatesusing linear correlation, (iii) identify two of the plurality ofcoordinates as associated with the two infrared reflectors using aKalman filter, and (iv) navigate the aerial vehicle toward said two ofthe plurality of coordinates associated with the two infrared reflectorsto enable the aerial vehicle to capture said arresting cable situated atthe landing site.
 2. The aerial vehicle of claim 1, wherein the onboardprocessor identifies a perching point on said arresting cable using saidtwo of the plurality of coordinates.
 3. The aerial vehicle of claim 2,wherein the aerial vehicle charges an onboard battery using powerreceived from said arresting cable via said arresting device.
 4. Avision-based navigation system for installation on an aerial vehicle,the vision-based navigation system comprising: a camera; an illuminatorsituated on the aerial vehicle to illuminate a landing site, wherein thelanding site comprises an arresting cable with two reflectors situatedon the arresting cable; an onboard processor to identify a perchingpoint at the landing site, wherein the onboard processor identifies theperching point by (i) generating a plurality of coordinates representingfeatures of the landing site using an image thresholding technique, (ii)identifying among said plurality of coordinates a coordinate associatedwith each of said two reflectors, and (iii) navigate the aerial vehicletoward the identified coordinates associated with each of said twoinfrared reflectors to enable the aerial vehicle to capture thearresting cable situated at the landing site.
 5. The vision-basednavigation system of claim 4, wherein the onboard processor isconfigured to identify said coordinate for each of said two reflectorsusing a Kalman filter.
 6. The vision-based navigation system of claim 4,wherein the onboard processor eliminates outlier coordinates from saidplurality of coordinates using linear correlation.
 7. The vision-basednavigation system of claim 4, wherein the onboard processor isconfigured to calculate a distance and a relative bank angle relative tothe arresting cable.
 8. The vision-based navigation system of claim 4,wherein the onboard processor is configured to calculate a relativepitch and heading of the aerial vehicle.
 9. The vision-based navigationsystem of claim 4, wherein the onboard processor is configured toidentify the perching point as a point approximately halfway between thecoordinates identified for said two reflectors.
 10. The vision-basednavigation system of claim 4, wherein the aerial vehicle furthercomprises an arresting device to capture the arresting cable at thelanding site.
 11. The vision-based navigation system of claim 10,wherein the arresting device comprises one or more conductive contactsfacilitate charging of the aerial vehicle via the arresting cable. 12.An aerial vehicle for autonomous landing, the aerial vehicle comprising:a fuselage; a camera; an illuminator situated on the aerial vehicle toilluminate two reflectors situated at a landing site; and an onboardprocessor to identify a perching point at the landing site, wherein theonboard processor identifies the perching point by (i) generating aplurality of coordinates representing features of the landing site usingan image thresholding technique, (ii) identifying among said pluralityof coordinates a coordinate associated with each of said two reflectors,and (iii) navigate the aerial vehicle toward the identified coordinatesassociated with each of said two infrared reflectors to enable theaerial vehicle to land at the perching point autonomously.
 13. Theaerial vehicle of claim 12, wherein the onboard processor is configuredto identify said coordinate for each of said two reflectors using aKalman filter.
 14. The aerial vehicle of claim 12, wherein the onboardprocessor is configured to eliminate one or more coordinates as outliercoordinates using linear correlation.
 15. The aerial vehicle of claim12, wherein the illuminator is an infrared illuminator and the tworeflectors are infrared reflectors situated on an arresting cable at thelanding site.
 16. The aerial vehicle of claim 12, wherein the onboardprocessor is configured to identify the perching point as a pointapproximately halfway between the coordinates identified for said tworeflectors.
 17. The aerial vehicle of claim 15, wherein the onboardprocessor is configured to calculate a relative bank angle and distancein relation to the arresting cable and to calculate a relative pitch andheading of the aerial vehicle.
 18. The aerial vehicle of claim 12,wherein the aerial vehicle further comprises an arresting device tocapture an arresting cable at the landing site.
 19. The aerial vehicleof claim 18, wherein the arresting device comprises one or moreconductive contacts facilitate charging of the aerial vehicle via thearresting cable.
 20. The aerial vehicle of claim 19, wherein the aerialvehicle charges an onboard battery using power received from thearresting cable via the arresting device.